This invention relates generally to stack injection molding and, more particularly, to a stack molding system having a plurality of valve gates commonly actuated by a uniform motion transferring mechanism.
In multi cavity stack injection molding systems, accurate control of resin melt flow from a hot runner manifold to all of the mold cavities is essential to achieving uniformity of the molded articles. The reciprocating valve pins used to control the gates to the cavities typically are operated simultaneously, which requires even loading of the valve pins. Compactness and simplicity of the machinery also are important considerations from the standpoint of cost, reliability and efficient heat transfer.
Representative examples of known stack injection molding systems are disclosed in U.S. Pat. Nos. 4,212,627; 4,244,909; 4,891,001; 5,013,235; 5,460,510; 5,478,230; and 3 5,533,882. Some of these employ a separate actuator for each valve pin, or a separate actuator for each opposed pair of valve pins. U.S. Pat. No. 4,212,627 discloses a stack molding arrangement wherein a single hydraulic actuator simultaneously moves all of the valve pins of two arrays of injection nozzles through a complex multi-link slide bar mechanism. This arrangement ensures simultaneous valve pin movement, but it tends to require frequent maintenance and does not permit any flexibility in operation, such as differential Opening or closing of the two arrays of injection nozzles.
In single-face molding machines various arrangements are known for simultaneously actuating a single array of valve pins. See, for example, U.S. 4,095,931 (sliding cam rod); 4,330,258 and WO 00/43187 (rack and pinion drive); and JP 9141688 (reciprocating plate). Other valve pin actuating mechanisms are disclosed in U.S. Pat. Nos. 4,378,963; 4,669,971; 4,712,995; 4,917,594; 4,923,387; 5,368,470; DE 3733363; DE 4230758; and DE 4231270. However, the technology used in such arrangements has not been of much benefit to stack molding apparatus, which generally tend to be complex, cumbersome, expensive, subject to premature wear, and/or unreliable. A need exists, therefore, for an improved stack molding apparatus that is durable and compact, allows for flexibility of operation, and efficiently and reliably produces molded products of good quality.
The present invention overcomes many of the disadvantages of the prior art by providing, in one aspect, an injection molding apparatus comprising a first array of injection nozzles and a second array of injection nozzles, each nozzle having a melt channel and a valve pin movable within the melt channel to open and close a mold gate. A melt distribution manifold is located between the first and second arrays of injection nozzles and is in fluid communication with the arrays of nozzles. Separate actuating assemblies are provided, one for displacing the valve pins of the first array of injection nozzles and another for displacing the valve pins of the second array of injection nozzles. Each actuating assembly comprises at least one actuator and a common linkage element driven by the actuator and linked to all of the valve pins of its respective array of injection nozzles to move the valve pins in unison.
In another aspect the invention provides an injection molding apparatus comprising an array of injection nozzles, and a melt distribution manifold in fluid communication with the array of injection nozzles. Each nozzle has a melt channel and a valve pin movable within the melt channel; and each valve pin has a driven portion and a tip end that controls melt flow through a mold gate. An actuating assembly for displacing the valve pins of the array of injection nozzles comprises at least one actuator and a common linkage element driven by the actuator and linked to the driven portions of all of the valve pins of the array of injection nozzles to move the valve pins in unison, the actuator being located between the common linkage element and the tip ends of the valve pins.
Further objects and advantages of the invention will appear from the following detailed description taken together with the accompanying drawing figures.